This invention relates to a thermostatic working element having a housing in which an electric resistance heating element is arranged whose electric connecting wires are sealingly guided through the bottom of the housing to the outside.
A thermostatic working element of the initially mentioned type is used particularly in connection with an electrically heatable thermostatic valve, as known, for example, from German Patent Document DE 42 33 913 Al (corresponding U.S. patent application Ser. No. 08/133,368, filed Oct. 8, 1993, now U.S. Pat. No. 5,385,296.
It is an object of the invention to provide a thermostatic working element of the initially mentioned type which has the shortest possible reaction time and is securely sealed off to the outside.
This object is achieved according to preferred embodiments of the invention in that the resistance heating element contains a carrier body to which a resistance coating is applied to which the connecting wires are soldered, and in that a base made of an insulating material is cast onto the carrier body in the area of the connecting wires, which base surrounds the connecting wires and is arranged in a sealing manner in the bottom area of the housing, and in that a sealing mass which seals off the base with respect to the housing is entered into the interior of the housing.
In the case of the thermostatic working element, the resistance heating element has a relatively large surface so that a good heat transfer takes place from the resistance heating element to an expansion medium housed in the housing. As a result, a relatively high heat input can be introduced into the expansion medium within a short time without the occurrence of very high temperatures in the resistance heating element which may lead to damage to other elements housed in the housing, particularly a bag-type, rubber-elastic membrane. By means of the base and the sealing mass, a good tightness is achieved so that also in the case of the occurring high pressures, it is reliably prevented that the expansion medium comes out of the housing. A silicone may, for example, be provided as the sealing mass. Thus, it is ensured that the good sealing is also maintained for an extended operating time.
In especially preferred embodiments of the invention, the base is provided with a projection which surrounds the connecting wires and which penetrates an opening of the bottom of the housing. As a result, the soldering points are relieved by which the connecting wires are soldered to the resistance layer.
In especially preferred embodiments of the invention, the base is provided with a collar inserted into the housing with a press fit. As a result, a further supplementary sealing is achieved while, in addition, the resistance heating element is securely fixed in the housing.
In especially preferred embodiments of the invention, it is provided that the carrier body has the shape of a plate which is centrically aligned with respect to the base.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.